The disclosure of Japanese Patent Application No. 2001-268355 filed on Sep. 5, 2001 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates generally to a fluid-filled active vibration damping device, which has a primary fluid chamber filled with a non-compressible fluid, and which is capable of actively offsetting or reducing vibrations applied to the primary fluid chamber by controlling a fluid pressure in the primary fluid chamber. More particularly, the present invention is concerned with such a fluid-filled active vibration damping device that is suitably applicable to an active elastic mount and an active dynamic damper or oscillator for use in automotive vehicles.
2. Description of the Related Art
Vibration damping devices have been used for damping or isolating vibrations (including noises induced by the vibrations) of a subject member such as a body of an automotive vehicle or other members suffering from these vibrations or noises. Known examples of such vibration damping devices include a vibration damping coupling or mount, e.g., an engine mount, which is interposed between the subject member and a vibration source, e.g., a power unit, so as to connect these two members in a vibration damping fashion for eliminating or reducing a vibration transmitted from the vibration source to the subject member; and a vibration damper that is fixed to the subject member for absorbing or reducing the vibration of the subject member.
A fluid-filled active vibration damping device has been proposed as one type of such vibration damping devices, as disclosed in JP-A-11-82611, JP-A-11-201220, JP-A-2000-356240. The known fluid-filled active vibration damping devices include: an elastic body elastically deformed due to vibrational loads applied thereto; a primary fluid chamber partially defined by the elastic body and an elastically displaceably movable member, while being filled with a non-compressible fluid; and a working air chamber formed on one side of the movable member that is remote from the other side on which the primary fluid chamber is formed. The pressure of the fluid in the primary fluid chamber varies due to the elastic deformation of the elastic body upon application of the vibrational loads to the elastic body, and is also actively controllable by applying a suitable air pressure variation to the working air chamber from the external area, which is transmitted to the primary fluid chamber via the movable member. Such a known fluid-filled active vibration damping device is capable of actively controlling a fluid pressure variation induced in the primary fluid chamber by applying an air pressure variation corresponding to a vibration to be damped, thereby exhibiting an active vibration damping effect or an offsetting effect with respect to vibrations excited in the subject member to which the fluid-filled active vibration damping device is installed.
Generally, the known fluid-filled active vibration damping device utilizes as a vacuum source a negative pressure available from an air intake port of an internal combustion engine, as discussed in the above-indicated documents, and the negative pressure of the vacuum source and the atmospheric pressure is alternately applied to the working air chamber for thereby inducing the air pressure variation in the working air chamber.
For ensuring the known fluid-filled active vibration damping device to exhibit an excellent damping effect with respect to vibrations to be damped, it is required to generate the air pressure variation whose magnitude corresponds to the magnitude of the vibrations to be damped. To meet this requirement, it has been studied to regulate the magnitude of the negative pressure transmitted from the negative pressure source to the working air chamber in an attempt to suitably regulate a range of air pressure variation extending between the atmospheric pressure and a given negative pressure, based on the actual magnitude of the vibrations excited in the subject member, which may be detected by means of an accelerator sensor or the like, or alternatively may be estimated according to a predetermined data map or the like. Namely, it has been considered to regulate the magnitude of the negative pressure applied to the working air chamber so as to generate the air pressure variation induced in the working air chamber, whose magnitude corresponds to that of vibrations excited in the subject member.
However, further extensive studies conducted by the present inventors reveals that when the level of the negative pressure is made higher (i.e., an absolute value of the negative pressure is increased), and the resultant air pressure variation induced in the working air chamber ranges from the atmospheric pressure to a relatively high level of the negative pressure, undesirable air pressure variation as a subordinate frequency component, which does not correspond to the vibrations to be damped, is prone to occur in the working air chamber, and undesirably is transmitted to the primary fluid chamber. This results in deterioration of the vibration damping characteristics of the fluid-filled active vibration damping device.
In addition, when the level of the negative pressure generated in the negative pressure source is made higher and the resultant air pressure variation induced in the working air chamber ranges over a wide negative pressure region, an amount of elastic deformation of the movable member is excessively increased, possibly deteriorating durability of the movable member.
It is therefore an object of the present invention to provide a fluid-filled active vibration damping device, which is novel in construction, and which is capable of inducing an air pressure variation having a large magnitude in an working air chamber, while preventing undesirable occurrence of an air pressure variation at a subordinate frequency range in the working air chamber.
The above and/or other objects of this invention may be attained according to at least one of the following modes of the invention. Each of these modes of the invention is numbered like the appended claims and depending from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the principle of the invention is not limited to these modes of the invention and combinations of the technical features, but may otherwise be recognized based on the teachings of the present invention disclosed in the entire specification and drawings or that may be recognized by those skilled in the art in the light of the present disclosure in its entirety.
(1) A fluid-filled active vibration damping device including: an elastic body elastically deformed due to vibrational loads applied thereto, a primary fluid chamber partially defined by the elastic body and filled with a non-compressible fluid; a movable member being elastically displaceable and partially defining the primary fluid chamber on one of opposite sides thereof; a working air chamber disposed an other of opposite sides of the movable member, which is remote from the primary fluid chamber; and a vacuum pump including an air intake port and an exhaust port that are connected to the working air chamber via a valve mechanism, wherein a fluid pressure variation in the primary fluid chamber is induced by an elastic deformation of the elastic body while being actively controlled by transmitting an air pressure variation applied to the working air chamber from an external area to the primary fluid chamber via the movable member, and wherein the valve mechanism is operable to perform a switching operation thereof for selectively applying a negative pressure generated in the air intake port and a positive pressure generated in the exhaust port to the working air chamber in order to generate the air pressure variation in the working air chamber.
In the fluid-filled active vibration damping device according to the present invention, the negative pressure generated in the air intake port of the vacuum pump and the positive pressure generated in the exhaust port of the vacuum pump are both utilized, namely, are selectively applied to the working air chamber. As a result, the air pressure variation induced in the working air chamber can range over the both sides of the atmospheric pressure, i.e., the negative pressure side and the positive pressure side located on the both sides of the atmospheric pressure as a central value of a range of the air pressure variation induced in the working air chamber, making it possible to induce the air pressure variation having a relatively large magnitude in the working air chamber, efficiently.
In the present mode of the invention, the air pressure induced in the working air chamber is arranged to vary across the opposite sides of the atmospheric pressure, namely, between a given negative pressure value and a given positive pressure value. This arrangement allows the movable member to be displaced more likely in a linear region where the movable member shows linear characteristics in a relationship between the applied load and the resultant spring constant of the movable member, rather than in a non-linear region where the movable member shows non-linear characteristics in the same relationship, in comparison with the case where the air pressure induced in the working air chamber varies between the atmospheric pressure and a given negative pressure value, even if these air pressure variations have the same magnitude. That is, the present arrangement prevents or minimizes the undesirable generation of the air pressure variation at a subordinate frequency range in the working air chamber, while making it possible to apply a relatively large magnitude of air pressure variation to the working air chamber. Thus, the fluid-filled active vibration damping device is capable of exhibiting an excellent vibration damping effect with respect to vibrations having a relatively large energy.
Moreover, the fluid-filled vibration damping device of the present mode of the invention includes the air pressure source adapted to apply air pressures to the working air chamber. This arrangement eliminates a need for utilizing a negative pressure available from an air intake system of the engine mount of an automotive vehicle, even if the fluid-filled active vibration damping device of the present invention is used in an automotive vehicle, making it possible to simplify the structure of an air conduit or an air piping system and to increase a degree of freedom in designing the conduit. Also, the present mode of the invention can provide a unit of a fluid-filled active vibration damping device equipped with an air source.
Any known vacuum pump may be employed as long as it is capable of generating a negative and a positive pressure of required level. Examples of the known vacuum pumps include a diaphragm type vacuum pump, a rocking piston type vacuum pump, a direct drive rotary vacuum pump, a sliding vane type vacuum pump, a scroll vacuum pump, a turbo type vacuum pump, a mechanical booster pump. In particular, the employable vacuum pump may be primary adapted to generate a negative pressure, or alternatively may be primary adapted to generate a positive pressure Various kinds of known air pressure pumps capable of generating a positive and a negative pressure as a result of an intake and an exhaust of air, may be employed as the vacuum pump in the vibration damping device of this mode of the invention. Similarly, any known valve mechanism may be employed as long as it is capable of alternately applying the negative pressure and positive pressure to the working air chamber. For instance, the valve mechanism may be constituted by a three-way valve that is operable to alternately connect the air intake port and the exhaust port of the vacuum pump to the working air chamber, or alternatively constituted by a plurality of valves, e.g., a first shutoff valve that is operable for connecting and disconnecting the working air chamber to and from the air intake port of the vacuum pump, and a second shutoff valve that is operable for connecting and disconnecting the working air chamber to and from the exhaust port of the vacuum pump.
(2) A fluid-filled active vibration damping device according to the above-indicated mode (1), wherein the working air chamber is connectable to the atmosphere via the valve mechanism, and the negative pressure generated in the air intake port, the positive pressure generated in the exhaust port and an atmospheric pressure in the atmosphere are selectively applied to the working air chamber based on the switching operation of the valve mechanism. This arrangement makes it possible to connect the working air chamber to the atmosphere as needed, for regulating the air pressure in the working air chamber, or alternatively for renewing the air pressure in the working air chamber to the atmospheric pressure, and makes it possible to select the pressure sources to be connected to the working air chamber, depending upon required vibration damping characteristics. For instance, the air pressure in the working air chamber may vary between the atmospheric pressure and a given negative pressure, or alternatively between the atmospheric pressure and a given positive pressure, depending upon the required vibration damping characteristics. Thus, the fluid-filled active vibration damping device can enjoy a far freedom in setting vibration damping characteristics thereof.
(3) A fluid-filled active vibration damping device according to the above-indicated mode (1) or (2), further comprising a negative pressure tank connected to a portion of an air conduit located between the air intake port of the vacuum pump and the valve mechanism, and a positive pressure tank connected to another portion of the air conduit located between the exhaust port of the vacuum pump and the valve mechanism. In the fluid-filled active vibration damping device constructed according to the present mode of the invention, the air pressure, i.e., the negative and the positive pressure generated in the vacuum pump is applied to the working air chamber via the negative and the positive pressure tank, respectively. This arrangement reduces or eliminates minute variations possibly induced in the negative and positive pressure generated in the vacuum pump due to the operation of the vacuum pump, thus making it possible to control air pressures applied to the working air chamber with high preciseness.
(4) A fluid-filled active vibration damping device according to any one of the above-indicated modes (1)-(3), further comprising a valve controller for controlling operation of the valve mechanism such that the valve mechanism alternately connects the working air chamber to the negative pressure generated in the air intake port and the positive pressure generated in the exhaust port at a frequency corresponding to that of vibrations to be damped, for generating the air pressure variation in the working air chamber. In this mode of the invention, the valve controller may be embodied by utilizing a known control device in which a signal detected from an accelerator sensor fixed to the subject member whose vibrations to be damped, or a signal corresponding to vibrations to be damped, e.g., an ignition pulse signal of the internal combustion engine, is utilized as a frequency reference signal, or a reference signal, for determining a phase of the switching operation of the valve mechanism with respect to the reference signal, based on a transfer function estimated on the basis of data of actual measurements of transfer function in advance, and the phase of the switching operation of the valve mechanism is controlled in a feedback fashion.
(5) A fluid-filled active vibration damping device according to any one of the above-indicated modes (1)-(4), wherein the vacuum pump comprises a vacuum pump of electromagnetically operated type, the vibration damping device further comprising: a pump output control device adapted to regulate an output of the vacuum pump of electromagnetically operated type depending upon magnitude of vibrations to be damped. In this mode of the invention, any known vacuum pumps indicated above with respect to the mode (1) of the invention, may be employed as long as it is operated by means of an electric motor. Preferably, a motor driven vacuum pump in which an electric motor is incorporated and an output of the electric motor is directly electrically controllable, may be employed. The pump output control device may be effectively embodied by utilizing a known control device, in which an output is controlled in a feedback or a feedforward fashion on the basis of a signal detected from an accelerator sensor fixed to the subject member for detecting a level of vibration excited in the subject member, or a signal obtained based on a predetermined operation formula or a data map that is prepared for estimating the excited vibration level from the operating condition of the internal combustion engine on the basis of a relationship between the operation condition of the internal combustion engine as a vibration source and the level of vibrations excited in the subject member, which were measured in advance.
(6) A fluid-filled active vibration damping device according to any one of the above-indicated modes (1)-(5), further comprising a pump synchronizing control device adapted to regulate a frequency and a phase of a variation of air pressure generated from the vacuum pump according to a frequency and a phase of the vibrations to be damped. While the vacuum pump is likely to suffer from a problem of generation of undesirable variation of generating pressure, like pulsations, this mode of the invention makes it possible to positively utilize the pulsation-like variation of the air pressure generated from the vacuum pump to improve damping capacity of the fluid-filled active vibration damping device. For instance, where the valve mechanism is controlled to be operated to generate in the working air chamber the air pressure variation whose frequency and phase correspond to those of vibrations to be damped, the variation of the air pressure generated from the vacuum pump may be adjusted in terms of its frequency and phase with respect to a frequency of subordinate vibrations, such as higher harmonics vibrations, which are prone to be derived from the primary vibrations to be damped. This arrangement enables the fluid-filled active vibration damping device to exhibit an excellent damping effect with respect to higher harmonics vibrations, although it is difficult to damp higher harmonics vibrations by simply controlling the operation of the valve mechanism.
(7) A fluid-filled active vibration damping device according to any one of the above-indicated modes (1)-(6), wherein the primary fluid chamber includes a pressure receiving chamber partially defined by the elastic body and an oscillating chamber partially defined by the movable member, the pressure receiving chamber and the oscillating chamber are held in fluid communication with each other via an orifice passage. In the fluid-filled active vibration damping device according to this mode of the invention, the fluid pressure variation induced in the oscillating chamber as a result of the displacement of the movable member is transmitted to the pressure receiving chamber through the orifice passage. With the help of resonance of the fluid flowing through the orifice passage, the fluid pressure variation induced in the oscillating chamber can be effectively transmitted to the pressure receiving chamber, thus making it possible to cause in the pressure receiving chamber a fluid pressure variation whose magnitude is made larger than that of the air pressure variation induced in the working air chamber.
(8) A fluid-filled active vibration damping device according to any one of the above-indicated modes (1)-(7), further comprising: a flexible layer partially defining an auxiliary fluid chamber being independent of the primary fluid chamber and filled with the non-compressible fluid; and a fluid passage for permitting a fluid communication between the primary fluid chamber and the auxiliary fluid chamber. According to this mode of the invention, when the elastic body is elastically deformed, the pressure of the fluid in the primary fluid chamber increases, causing flows of the non-compressible fluid through the fluid passage based on the pressure difference between the primary fluid chamber and the auxiliary fluid chamber. With the help of resonance of the fluid flowing through the fluid passage, the fluid-filled active vibration damping device can exhibit passive vibration damping device with respect to vibrations whose frequency is held within a frequency band to which the fluid passage is tuned. For assuring the passive damping effect owing to resonance of the fluid flowing through the fluid passage with high efficiency, a resonance frequency of the fluid flowing through the fluid passage, in other words, a frequency of vibration to be damped with the help of the passive damping effect based on resonance of the fluid-flowing through the fluid passage, is set to a frequency band that is lower than a frequency of vibration to be damped with the help of active damping effect based on displacement of the movable member.
(9) A fluid-filled active vibration damping device according to any one of the above-indicated modes (1)-(8), further comprising a first mounting member and a second mounting member that are elastically connected with each other via the elastic body, wherein the first mounting member is adapted to be attached to a vibrative member and the second mounting member is adapted to be attached to a subject member whose vibrations to be damped so that the vibration damping device is interposed between the vibrative member and the subject member for elastically connecting the vibrative member and the subject member in a vibration damping fashion. The fluid-filled active vibration damping device according to this mode of the invention can effectively provide vibration-damping devices for use in an automotive vehicle, such as an engine mount, a differential mount, a body mount, a suspension mount and a suspension bushing.
(10) A fluid-filled active vibration damping device according to any one of the above-indicated modes (1)-(9), further comprising a support member and a mass member that are elastically connected with each other via the elastic body, the support member being adapted to attached to the subject member whose vibrations to be damped such that the mass member is elastically supported by the subject member via the elastic body In the fluid-filled active vibration damping device constructed according to this mode of the invention, the elastic body as a spring component and the mass member as a mass component cooperate to form one vibration system. An application of the air pressure variation to the working air chamber oscillates this vibration system, and the resonance of this vibration system is effectively utilized to apply an oscillating force corresponding to the vibrations to be damped to the subject member, so that an active vibration damper capable of offsetting or actively damping vibrations is effectively provided.